I have a 1995 Blazer with the L35 "W" code 4.3. It runs poorly at idle and lopes at cruising speed. It's throwing an engine check light. I took it to my shop and they said the computer was shot because their scanner wouldn't link with it. I bought a used ECM, installed it, the light cleared then came back. I bought my own OBDII code reader and even with the new ECM I can't establish a link.

Any suggestions would be appreciated. I have the 1995 GM Service manual and OBDII supplement but they're not much help at this point.

 

Welcome to the OBD1.5 PCM. It is not fully OBD2, nor is it OBD1. Rather, it is a mix of the two and not supported by 95% of the scanners available. I am surprised that your shop did not know this.

As far as your condition, I would start with a fuel pressure test, specifically watching the pressure after you prime the system, then turn the key off. The fuel pressure test port is located near the brake booster on the back of the intake plenum. It has a schrader valve connection where you can screw on a test gauge. The pressure should run about 55-60psi with the key on and should not drop more than a few psi when you turn the key off. If it drops and continues down to zero, then the FPR (fuel pressure regulator) is the likely cause.